The present invention relates to a drilling motor, such as a downhole drilling motor, that operates pursuant to the Moineau principle for drilling deep holes or wells in the ground. A helically extending rotor is disposed within a stator, and the rigid shell of the stator is provided with an inwardly helically extending lining of elastomeric material for receiving the rotor, wherein the shell is provided with essentially cylindrical end sections having a preferably slightly conical inner thread for the securement of connection elements of the drilling motor.
With heretofore known drilling motors of this type, the shell of the stator is cylindrical on the outside; the outer diameter of the end sections corresponds to the diameter of the portion that is disposed between them and that surrounds the elastomeric lining. As a consequence, very different thicknesses result for the elastomeric lining over the length of the stator; these differing thicknesses represent an unnecessary material expense for the elastomer, which in addition is unfavorably stressed.
It is therefore an object of the present invention to at least to a large extent eliminate these drawbacks, and in addition to also preclude drawbacks that result during the operation of the drilling motor upon return of the pressurized drilling fluid.